WASHINGTON - Former president George Bush, a gun enthusiast and decades-long member of the National Rifle Association, has resigned from the group because of its statements that agents of the Bureau of Alcohol, Tobacco and Firearms are "jackbooted thugs" who harass gun owners.

"Your broadside against federal agents deeply offends my own sense of decency and honor, and it offends my concept of service to country," Bush wrote to NRA president Thomas Washington in a May 3 letter that was released yesterday. "It indirectly slurs a wide array of government law-enforcement officials, who are out there, day and night, laying their lives on the line for all of us."

Bush said NRA executive vice president Wayne LaPierre's description of federal agents as " `wearing Nazi bucket helmets and black storm trooper uniforms' (and) wanting to `attack law-abiding citizens' is a vicious slander on good people." LaPierre used the description in a fund-raising letter sent to the NRA's 3.5 million members early this year, and he defended it in the wake of the April 19 bombing of the federal building in Oklahoma City.

The Fairfax, Va.-based NRA, which has 3.4 million members, endorsed Bush in 1988 but made no presidential endorsement in 1992.

As an elected official, Bush frequently supported the NRA's aims, including its opposition to the ban on assault weapons that Congress passed last year. In his letter, Bush said he was "a gun owner and an avid hunter" who had "agreed with most of NRA's objectives, particularly your educational and training efforts, and your fundamental stance in favor of owning guns."

But his resignation letter was more personal than political.

"Al Whicher, who served on my (Secret Service) detail when I was vice president and president, was killed in Oklahoma City," Bush wrote. "He was no Nazi. He was a kind man, a loving parent, a man dedicated to serving his country - and serve it well he did.

"In 1993, I attended the wake for ATF agent Steve Willis, another dedicated officer who did his duty. I can assure you that this honorable man, killed by weird cultists, was no Nazi." Willis was one of four federal agents killed in the initial February 1993 raid on the Branch Davidian compound near Waco, Tex.

"John Magaw, who used to head the (Secret Service) and now heads ATF, is one of the most principled, decent men I have ever known," Bush wrote. "He would be the last to condone the kind of illegal behavior your ugly letter charges. The same is true for the FBI's able Director Louis Freeh. I appointed Mr. Freeh to the federal bench. His integrity and honor are beyond question."

The letter concluded, "You have not repudiated Mr. LaPierre's unwarranted attack. Therefore, I resign as a life member of NRA, said resignation to be effective upon your receipt of this letter. Please remove my name from your membership list. Sincerely, George Bush."

Last night the NRA's president, Washington, sent Bush a five-page letter in reply, asking him to withdraw his resignation until Congress investigates cases of what the NRA contends is ATF abuse. "I'm sorry that you have chosen to unequivocally condemn NRA's words without first seeking an explanation," Washington wrote. Recalling that the Reagan-Bush administration placed some restraints on ATF after NRA criticism in the early 1980s, Washington asked, "Have you forgotten, President Bush, your previous passion for justice and fairness for all law-abiding citizens?"

ATF officials were exuberant about Bush's statement. "All ATF personnel, from the director on down, are very appreciative of President Bush's statement of support for all law enforcement," said spokesman Jack Killorin. He added that no one in the agency lobbied Bush to take the action.